Option (iv) is the answer.
Alcohols have a lower acidity level than phenol. Furthermore, electron-withdrawing groups make phenols more acidic, therefore m-chlorophenol is the most acidic.
Which of the following is most acidic? (i) Benzyl alcohol (ii) Cyclohexanol (iii) Phenol (iv) m-Chlorophenol
Which of the following is most acidic? (i) Benzyl alcohol (ii) Cyclohexanol (iii) Phenol (iv) m-Chlorophenol